Step positioning device



Aug. 27, 1957 w. A. BLACK ETAL 2,804,555

STEP POSITIONING DEVICE Filed Oct. 19, 1953 s Sheets-Sheet 1 K z v-3 -r-4 k /,I

as 43 20 26 V 0" q 74 ed !e 28 fl I 42 as i CA. BIa=s-\ (Everett Q5. was? 1957 w. A. BLACK ET AL STEP POSITIONING DEVICE 5 Sheets-Sheet 2 Filed Oct. 19, 1955 Aug. 27, 1957 Filed 001;. 19. 1953 w. A. BLACK ET AL 2,804,555

STEP POSITIONING DEVICE 5 Sheets-Sheet 3 @[LH'Lom CH. mzalck lverett. Mask- Aug. 27, 1957 w. A. BLACK ET AL STEP POSITIONING DEVICE 5 Sheets-Sheet 4 Filed Oct. 19, 1955 raven-rein:

CATQmEY 7, 957 w. A. BLACK ET AL 2,804,555

STEP POSITIONING DEVICE I Filed Oct. 19, 1953 5 -Shee 5 zseasss STEP PUSKTIONENG DEVICE William A. Black, Montclair, N. 1., and Everett J. West,

Huntington, N. Y., assignors to General Qorporation, New York, N. Y., a corporation of Delaware Application Uctoher 19, 1953, Serial No. 336,811

' 13 Claims. (c1. sis-4s The present invention. relates in general to step positioning devices "and in particular to remotely controlled magnetically actuated ratchet mechanisms for rotatably indexing a shaft by stepping it in either direction.

To illustrate an exemplary application in which the invention finds especially advantageous use, it may be It often happens that the elapsed time from dropping to detonation must be changed while the plane is in flight, that is, after the bombs have been originally set and loaded into the plane. But this is a time consuming and tedious operation at best when done manually; and often the bombs are inaccessible for its accomplishment once they have been loaded into a plane.

The need arises, therefore, for a step positioning device to set the time dials, i. e., to index their shafts, from a remote point, e. g., the pilots cockpit, in a bombing plane. It must be small and compact to fit in the nose of a bomb; it must be unaffected by the accelerational forces of extreme shock and vibration, remaining positively locked in the desired setting; it must be settable with a minimum of torque, that is to say, a minimum of actuating current; and it must be absolutely reliable in its action to assure that the time fuse is accurately set.

It is the general aim of the present invention to provide a step positioning device of general utility which fulfills all of the requirements enumerated above.

More specifically, it is an object of the invention to provide an improved step positioning device for rotatably indexing the shaft in one direction or the other in response to positive or negative electric current pulses In the illustrative ap-.

supplied from a remote point. plication described, each bomb is provided with a pair of electrical connections, ripped free when the bomb is dropped, through which a pilot, for example, may cause a certain number of pulses to be sent to thereby effect the desired setting of the time dial and its shaft.

It is another object of the invention to provide a novel device for step positioning a shaft which positively locks the shaft in a selected rotational position, yet which may be shifted to unlock the shaft for manual setting, if desired.

A further object is to provide such a device having a compact ratchet mechanism extremely reliable in its stepping and locking action. ity, it is an object to provide a ratchet mechanism having two actuating pawls and two locking pawls all moved The requirements for such a device are stringent.

In achieving such reliabil- 7 2,8h4,555 Patented Aug. 2?, 1957 or released, respectively, upon the rotation of a single member.

An additional object is to provide an improved electromagnetic arrangement for urging the ratchet mechanism to step the shaft in either direction, the armature thereof being a cylindrical permanent magnet held normally in a central or balanced position between two limits of rotation.

Other objects and advantages will become apparent as the following description proceeds, taken in conjunc sentation, of the actuating pawls, their mounting, and

their actuating link means;

Fig. 8 is a right side elevation of the device, showing in dashed outline the return mechanism for centering the actuating pawls and magnet rotor;

Fig. 9 is a detail view, in exploded perspective representation, of the locking pawls and their organization;

and I Fig. 10 is a detail View, in perspective, of the return or centering mechanism.

While the invention has been shown and is described in some detail with reference to a particular embodiment thereof, there is no intention that it be thus limited. On the contrary, it is intended here to cover all alterations, modifications, and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Turning now to the illustrated embodiment of the invention, it will be seen that the stepping mechanism here shown is included within a frame 20 having end plates 21, 22 separated by suitable spacers (Fig. 1). An output shaft 23 which is to be steppingly positioned in one direction or the other by means to be described extends for journal support between the two end plates 21, 22. The output shaft 23 is surrounded by an input shaft 24, the rotational oscillations of which drive the stepping mechanism. I

For oscillating the input shaft'24- a magnetic struc ture is provided including a laminated stator 25 rigidly mounted within the frame it? and a centrally disposed rotor 26 cooperating therewith (Figs. 1 and 2). The rotor 26 is cylindrical in shape and permanently magnetized to have diametrically opposite north and south poles as shown. Additionally, the rotor 26 is rigidly mounted on the input shaft 234 to rotate the latter in response to magnetic forces created by the stator 25.

For this latter purpose the stator is slotted to receive a pair of electromagnetic windings or coils 27, 28, respectively. The stator 25 provides two pairs of diametrically opposed north and south poles. A magnetic field is created between these poles through the rotor 26 upon current being supplied through the coils 27, 28, the polarity or direction of such field being dependent upon the sense of the current. In Fig. 2 the polarity of such magnetic fields for a positive pulse of current has been indicated, such current pulse being effective to rock the rotor clockwise by magnetic attraction and repulsion. A

negative pulse of current cause a reversal of the polarities indicated, with the result that the rotor 26 will rock counterclockwise, such oscillating rotational movement 3 being transferred through the input shaft 24 to drive the stepping mechanism.

The right end (Fig. 1) of the output shaft 23 carries a rigid toothed wheel 34 having'its periphery formed with a series of spaced, radially projecting teeth 35 (see also Figs. 3 and 4). For advancing the toothed wheel 34 in one direction or the other, two drive pawl members, 36 and 36a are provided, each pivoted at its central portion and each having oppositely extending pawls, 37, 38 and 37a, 38a, respectively. Means are provided for supporting the pawl members 36 and 36a for limited bodily movement about the periphery of the toothed wheel 34 and for restoring the. to their central or neutral positions shown in Fig. 3. The supporting means includes arotatably mounted support plate 39 having axially extending pintles 4-0 and 46a on which the pawl members 36 and 36a are pivotally received.

Resilient centering of the support plate 39 is effected by the centering mechanism shown most clearly in Figs. 8 and 10. Such centering mechanism includes a pair of posts 41, 42 extending outwardly fromand swingable with the support plate 39. These movable posts 41, 42 are in respective radial alinement with a pair of stationary posts 43, 4 on the end plate 21. Means are provided for resiliently restraining and restoring'the movable posts 41, 42 into alinement with the fixed posts 43, 44. The latter is accomplished by a pair of centering members or levers 4-5, .6 which haveoverlapping ends 47, 48 and 47a and 48a, defining alined openings 51, 52, and 53, 54. Springs 55, 56 are attached to thecentering members 45, 46, respectively, urging them outwardly and thereby maintaining all of the posts in alinement. Rocking of the support plate 39 in either direction is resiliently opposed, with the result that the plate 39 and the pawl members36 and 36:: mounted thereon are normally maintained in the centered position shown in Fig. 3.

As here shown, the movable posts 41 and 42 may be provided as extensions of the pintles it and 46a, respectively (Fig. l), and post 41 may extend additionally into an arcuate slot 53 defined in the end plate 21. The support plate 39 is thus limited in the extent of its freedom for rotation in either direction by either end of the slot 58. The latter is made of such extent that the toothed wheel 34 will be advanced one step, i. e., one tooth, before the post 41 strikes the end of the slot 58.

For accomplishing the unique stepping operation to be more fully described, a rocker connection is provided between the input shaft 24 and the drive pawl members 36 and 36a, subjecting the pawl members sequentially to rocking movement about the pintles 4e and 40a and bodily advancement about the periphery of toothed wheel 34. Referring especially to 'Fig. 3, this rocker connection is indicated at 59 and is here eifected by two arms 60 and 60a each terminating in a single tooth. These teeth register with the toothed segments 61 and 61a, respectively, formed on the pawl members 36 and 36a. The arms 60 and 6001 are rigid with the input shaft 24, extending radially outward therefrom. When the input shaft 24- is rotated through a small angle by energization of the magnetic actuator mechanism, the torque will be transferred from the arms 6t) and 66a to the arms 61 and 61a. Because of the resistance provided by the centering mechanism and a positive locking arrangement described below, the support plate tends to remain stationary, and such torque therefore causes the drive pawl members to rock about the pintles 46 and 41, thus placing one of the pawls 37 or 33 and 37a or 38a (depending upon the direction of rotation) in engagement with the toothed wheel 34 and unlocking the above mentioned locking mechanism. Additional rotation of the input shaft 24 overpowers the centering mechanism so that the support plate 39 and the pawl members 36 and 36a thereon rotate bodily, carrying the toothed wheel 34 along through one step of movement. That is to say, the initial rocking of the pawl members 36 and 36a brings pawls 37 and 37a or 33 and 33a into engagement with the teeth 35, preventing further rocking and resulting in the engaged pawls dragging the toothed wheel 34 and output shaft 23 through one rotational step, as determined by the post 41 striking the end of slot 58. After the torque on the input shaft 24 is released, due to deenergization of the coils 27, 23, the centering mechanism becomes effective to restore the support plate 39 to the central position indicated in Fig. 3.

In further accomplishing the objects of the invention, means are provided for normally locking the toothed wheel 34 in its center position and in any of its rotational positions and for releasing it for stepping rotation in response to the rocking movement of the pawl members 36 and 36a, i. e., just after the drive pawls engage the toothed wheel 34. Such means include two lockingpawl members 65 and 65a pivoted on the end plate 21 and having integral pawls 66 and 66a and operating arms 67 and 67a, respectively, the latter extending into the paths of rocking movement of the pawl member 36 and 36a (see Fig. 3). The locking pawl member 65 has its pawl 66 biased into locking engagement with the teeth of toothed wheel 3'4 by a'spring 68 and the locking pawl member 65a has its pawl 664: so biased by spring 68a.

The support plate 39 has two laterally extending arms 80 and 80a which project just beyond the extremities of teeth 35 on gear 34. The pawls 66 and 66a are of sufficient thickness to engage the teeth 35 and also extend into the paths of movement of arms 80 and 8611. In the normal position of the mechanism, pawls 66 and 66a are in locking engagement with gear 34 and also engage the edges of arms and 86a, respectively, to positively lock the support plate 39 against movement.

It will be apparent, therefore, that upon initial movement of input shaft 24 in a clockwise direction, the plate 39 is held by pawls 66 and 66a. This results in rocking movement of the pawl members 36 and 36a through the linkages 60, 61 and 60a and 61a, respectively. As these members begin to turn in a counterclockwise direction, arm 37 engages arm 67 of member 65 causing it to rotate in a clockwise direction and withdraw locking pawl 66 from the teeth of gear 34. Similarly, the right hand arm of pawl member 36a engages arm 73a causing it to rotate in a clockwise direction, which motion is transmitted through linkage 71a-72a to member 65a. Rotation of member 65a in a counterclockwise direction withdraws locking pawl66a from gear 34.

The ends of the arms, such as 67, beveled so that the pawls (in the assumed case pawls 37 and 37a) engage the gear teeth 35 before the locking pawls 66 and 66a release 'the gear 34 and the support plate 39. After the latter poles of rotor 26 opposite the air gaps 29 and 30, restore the parts to normal position. 7 As soon as the armature starts its return movement, it rocks the pawl members 36 and 36a allowing the arms 67 and 73a to be moved toward normal position by springs 68 and 68a. In the assumed case, this permits pawl 66 to engage the teeth of gear 34 to lock same in the advanced position before pawls 37 and 37a are removed from engagement with teeth 35. The plate 39 and the associated pawl members 36 and 36a are then returned to normal position by the centering mechanism described above and illustrated intFigs. 8 and 10.

As noted above one of the drive pawls 37, 38 and one of the pawls 37a, 38a are engaged with the gear 34 ir respective of the direction of rotation of shaft 24. Also, both locking pawls 66 and 66a are positively controlled regardless of the direction of rotation. The latter is accomplished by duplicate rocker and linkage mechanism 67, 72, '71, 70, 73 and 67a, 72a, 71a, 70a, 73a as described below.

The rocker element 70 is pivoted on the end plate 21 and includes a toothed arm 71 in the nature of a mutilated gear extending for registry with a mating arm 72 integral with the locking pawl member 65. The element 70 and member 65 thus swing together in opposite directions of rotation by virtue of their rocker connection, both being biased by the spring 68 which interconnects them. The element 70 further includes an actuating arm 73. disposed in the rocking path of the left end of the pawl member 36a as well as an inwardly extending release arm 74. a a

A corresponding rocker element 70a is identical in construction and connection to the element 70, having a toothed arm 71a registering with an integral arm 72a of the locking pawl member 65a, and an operating arm 73a.

disposed in the rocking path of the right end of the paw member 36a.

Upon clockwise rotation of the input shaft 24, the pawl member 36a is rocked counterclockwise in its initial movement so that its right extremity strikes the operating arm 73a and swings the locking pawl member 65a counterclockwise to withdraw its pawl 66a from the toothed wheel 34. As explained previously, upon such clockwise rotation of the input shaft, the rocking of the pawl member 36 resulted in its left extremity striking the operating arm 67 to withdraw the locking pawl 66 on the wheel. Thus, upon further rotation of the input shaft, and bodily rotation of the pawl members 36 and 36a with the support plate 3'9, the pawls 37 and 37a, which are, in engagement with the toothed wheel 34, ro-

tate it one step in a clockwise direction until the mova ble post 41 strikes the end of slot 58. .The return mechanism then recenters the parts to the positions shown by Fig. 3 upon removal of the rotational torque from the input shaft as described above.

It will be clear from the drawings that the symmetry of the device makes possible the extension of the pintle 40a to provide the second movable post 42 for the return mechanism. This post 42, in addition, may extend into a second arcuate slot 58a defined in the end plate 21 at a position diametrically opposite the corresponding slot 58. From the symmetry of the device as described, it will also be understood that upon counterclockwise rotation of the input shaft 24, as occasioned by a negative pulse applied to the coils 2'7, 23, the rocker connections 53, 59a result in the initial rocking of the drive pawl members 36, 36a in clockwise directions. As a result, the right extremity of pawl member 36 strikes the operating arm 67a and the left extremity of pawl member 36a strikes the operating arm 73 to withdraw the locking pawls 66 and 66a. Further bodily rotation of the pawl members 36, 36a result in their pawls 38 and 38a carrying the toothed wheel 34- one rotational step in a counterclockwise direction.

From the foregoing, it is believed that the organization and operation of the illustrated embodiment of the invention will now be clear. The output shaft 23 is positively locked in any of its several rotational positions by the engagement of not one, but two, locking pawls 66, 66:1. And, upon energization of the coils 27, 23 the magnetic torque produced upon the magnet rotor 26 rotationally displaces the input shaft 24 in either direction according to the polarity of the energizing current, within the limits afforded by arcuate slots 58, 58a. This results in the release of both of the locking pawls through the striking of one of the auxiliary elements 7ft or 70a and one of the locking pawl members 65 and 65a by the drive pawlmembers 36 and 36a. Just before such release, two of the drive pawls 37, 37a and 38, 38a are engaged with the toothed wheel 34, to rotate it through one stepupon the bodily rotation of the drive pawl members 36, 36a with the support'plate 39; Such. stepping may thus be effected from a remote point by supplying the coils with positive or negative current pulses, the output shaft 23 thus being indexed to any desired setting.

- The invention further contemplates the manual setting of the output shaft 23 to any of its rotational positions."

pawls 66, 6611.; The output shaft 23, or some element such as the dial carried thereby, may then be manually rotated .to anydesired position. Withdrawal of the.

release pin then lets the locking pawls 66, 66a snap back into engagement with the toothed wheel 34 to secure the output shaft 23 in the position at which it has been set.-

We claim as our invention:

1. In a device for indexing a shaft in response to remotely originated electric signals, the combination comprising a frame journaling the shaft, a cylindrical magnet rotor having diametrically opposed north and south poles rotatably disposed on the shaft, an electromagnetic stator and winding carried by said frame and disposed to urge rotation of said rotor in opposite directions upon energization with positive and negative voltage and current pulses, a toothed wheel rigid with said shaft, a spring-centered support plate journaled for limited rotation on said shaft, a pair of drive pawl members pivoted on said plate at diametrically opposed sides of said wheel, said drive pawl members each having pawls at their opposite extremities, a pair of locking pawls carried by said frame on diametrically opposed sides of said wheel, means urging said locking pawls into engagement with said wheel, rocker link connections between said drive pawl members and said locking pawls for withdrawing the latter from said ratchet upon rotation of said magnet, and rocker links between said magnet and said drive pawl members whereby rotation of said magnet first rocks said drive pawl members to swing said locking pawls free of said wheel and one of their drive pawls into engagement with said wheel, and, secondly, moves said pawl members bodily to advance the wheel one step.

2. In a remotely controlled step-positioning device for indexing an output shaft, the combination comprising a frame journaling the shaft, a spring-centered input shaft rotatably disposed on said output shaft, 9. cylindrical magnet having diametrically opposed north and south poles fast with said input shaft, an electromagnetic winding carried by said frame and disposed in spaced relation to said magnet to urge the rotation of said input shaft in opposite directions upon energization by positive and negative currents respectively, a toothed wheel rigid with said shaft, a pair of drive pawl members positioned on diametrically opposite sides of said ratchet, a pair of locking pawls positioned on diametrically opposite sides of said ratchet, and means linking said drive pawl members and locking pawls to said input shaft to release the latter from and engage the former with said wheel to rotate the output shaft upon limited rotation of said magnet from a central position in response to energization of said winding.

3. A two-way step positioning device comprising, in combination, a frame, a shaft to be indexed journaled in said frame, a toothed wheel rigid with said shaft, a.

spring-centered support plate rotatable between limits on said shaft, a pair of drive pawls 'pivotedon said support plate at diametrically opposite sides of said wheehmeans for pivoting saiddrive pawls into engagement with said wheel and thence rotating said plate to step said shaft in either direction, a pair of locking pawl assemblies at diametrically opposite sides of said -wheel, each said assembly comprising a locking pawl andan auxiliary element pivoted on said frame, rocker means linking said locking pawl and auxiliary element to swing in opposite directions, said drive pawls and locking pawl assemblies having cooperating arms, the first of said drive pawls striking-one or the other of said locking members as it ispivoted in one direction or-another, and the second of-said drive pawls striking one or-the otherhof the arms on said auxiliary element as it is pivoted in one direction or another,-the locking teeth of said locking pawls being.thereby--withdrawn from said ratchet. a 7

. 4. Aimechanism for positioning a shaft stepby step which comprises an actuator mounted for oscillation within a limited range of ea-chside of a center position, a. toothedoutput wheel arranged coaxially with respect to said actuator, a drive pawl member having a central pivot and having pawls at its opposite ends'for engaging said output wheel, a spring-centered support *member connected to the pivot of the pawl member for 'bodilytransporting the pawl member about'the periphery of-the output wheel, and a rocker connection between-the actuator and said pawl member whereby 'upon' rotation of the actuator the pawl member sequentially (1) rocks one of its pawls into engagement with the toothed wheel, and then upon-continued rotation (2) moves the pawlmember bodily to advance the toothed wheel through one step of movement.

5. A mechanism for positioning a shaft step by step which comprises an actuator mounted for oscillation within a limited range on each side of -a central position, a toothed output wheel arranged coaxially with respect to said actuator, a drive-pawl member having a central pivot and having pawls at its opposite ends for engaging said output wheel, -a spring-centered support member connected to the pivot of the pawl member for bodily transporting the pawl member about the periphery of theoutput Wheel, a locking pawl normally in locking engagement with the output wheel but having means coupled to the drive pawl member for unlocking the same in response to rocking movement of the pawl member, and a rocker connection between the actuator and said pawl member whereby upon rotation of the actuator the pawl member sequentially (l) rocks one of its pawls into engagement with the toothed wheel, and then upon continued rotation (2) moves the'pawl member bodily to advance the toothed wheel through one step of movement.

6. In a mechanism for step positioning an output shaft, the combination comprising a toothed Wheel rigid with the output shaft, a drive pawl member having a central pivot and pawls at its opposite ends for engaging said output wheel, a spring-centered support member carrying said drive pawl member, an actuator, rocker means connecting said actuator and said drive pawl member to (1) rock said pawl member into engagement with said wheel, and (2) .bodily rotate said pawl member with said support member to rotationally step said .output wheel, a spring-biased locking pawl member having a locking pawl urged into engagement with said wheel, said locking pawl member having an operating arm disposed in the rocking path of said drive pawl member to thereby have its locking pawl withdrawn from said wheel prior to the bodily rotation of said drive pawl member.

7. In amechanism for step positioning an outputshaft, the. combination comprisinga toothed wheel rigid with theoutput shaft, apair ofdrive pawl members each having a pair of pawls for engaging said wheel, means pivotally mounting said drive pawl members, said'means being rotatable to bodily rotate said drive pawl'members, a-pair of locking pawl members each having locking pawls-normally engaged with said wheel, a pair of auxiliary rocker elements connected respectively to said locking pawl members, and means on said locking pawl members and said rocker elements disposed in the pivoting paths of said drive pawl members to unlock said locking pawl upon pivoting of the drive pawl members.

8. In a step positioning'device having a shaft journaled in a frame, indexing means for said shaft comprising, in combination, a toothed wheel rigid with said shaft, 21 supportplate keyed to, said frame for limited rotation ineither direction relative thereto, a pair of two-way drive pawls carried by said support plate, an actuator rotatably disposed on said shaft and adapted to be rotated in either direction, rocker link means connecting said actuator to said drive pawls to effect engagement of the latter with said wheel and rotation thereof within the limits of said support plate, a pair of locking pawls carried by said frame and biased into locking engagement with said wheel, rocker link connections between said drive pawls and said'locking pawls for withdrawing the latter from said wheel upon rotation of said actuator from a central position, and resilient biasing means for returning said support plate and actuator to a central position between their rotational limits.

9. In a two-way step positioning device having an output shaft to be rotatably indexed, an input shaft rotatable between limits on the output shaft, and a ratchet mechanism operative to step the output shaft upon rotation of the input shaft in either direction from a centered position, means for imparting such limited rotation to the input shaft comprising, in combination, a cylindrical magnet fast on the input shaft, said magnet having diametrically opposite north and south poles, at magnetically permeable stator surrounding said cylindrical magnet and having two axially extending radial air gaps immediately opposite said north and south poles, respectively, and a pair of electric coils on said stator for magnetically polarizing said air gaps upon electric current being supplied therethrough, the sense of such polarization and the direction of resulting rotation of said magnet being dependent upon the direction of current supplied through said coils.

10. In a two-way step positioning device having an output shaft to be indexed, an input shaft rotatable between limits on the output shaft, and a ratched mechanism operative to step the shaft upon rotational oscillation of the input shaft in either direction from a centered position, a return mechanism for biasing said input shaft to its centered position comprising, in combination, a plate rotatable on said shaft and linked to said input shaft, a frame member journaling the output shaft, a pair of spaced posts swingable with said plate, a pairof stationary postsextending axially from said frame member andspaced radially inward with relation to respective ones of said swingable posts, a pair of centering members extending to engage opposite sides of said swingable and stationary posts, means biasing said centering members in opposite outward directions and into such engagement with said posts, rotation of said plate in either direction thereby pivoting said members about different ones of said stationary posts against said biasing means, the plate being returned to its centered position by opposite ends of said centering members bearing against different ones of swingable posts.

11. In a mechanism for step positioning an output shaft, the combination comprising a toothed wheel rigid with the output shaft, a support member rotatable about said shaft, a drive pawl member on said support member and adapted to engage said wheel and rotationally I displace it upon rotation ofthe support member, a pair of movable posts diametrically located on said support member relative to the axis of the output shaft, a pair of stationary posts located in radial alinement with respective ones of said movable posts, a pair of return members having overlapping end portions embracing said posts, and resilient means urging said return members in opposite directions to restrain and return said posts to radial alinement, and to thereby return said support member to a central position when displaced therefrom.

12. In a mechanism for step positioning an output shaft, the combination comprising a toothed wheel rigid with the output shaft, a drive pawl member having a central pivot and pawls at its opposite ends for engaging said output wheel, a spring-centered support member carrying said drive pawl member, an actuator, rocker means connecting said actuator and said drive pawl member to (1) rock said pawl member into engagement with said wheel, and (2) bodily rotate said pawl member with said support member to rotationally step said output wheel, a lock arm on said support member, a spring-biased locking pawl member having a locking pawl normally engaging said wheel and said lock arm to hold said wheel and said support member in locked positions, and means operated by the rocking movement of said drive pawl member for removing said locking pawl from looking engagement with said wheel and said lock arm of said support member prior to the bodily rotation of said drive pawl member.

13. In a step-by-step mechanism, a toothed wheel rigidly mounted on an output shaft, a drive pawl for engaging said wheel, a support plate pivotally mounting said drive pawl, said plate being mounted on said output shaft for limited rotation thereon, a lock arm on said support plate, a lock pawl normally engaging said wheel and said lock arm to maintain same in locked position, means coupled to said driving pawl for rotating same on its pivot to engage said wheel and thereafter rotating said support plate to advance said wheel, and means operated by the rotation of said drive pawl on its pivot for releasing said lock pawl from engagement with said wheel and said lock arm.

References Cited in the file of this patent UNITED STATES PATENTS 313,967 Tifiany Mar. 17, 1885 1,645,136 Goldsmith et a1. Oct. 11, 1927 2,427,621 Peterson Sept. 16, 1947 

